Process for preparing granules of pigments by means of double extrusion

ABSTRACT

A process for the production of a particle composition containing, at least one resin and at least one pigment is described, said process comprising the following steps: *extrusion of a mixture containing said at least one resin and said at least one pigment without induced heating; *subsequent extrusion, with induced heating, of the mixture obtained from the preceding extrusion; *granulation of the mixture thus obtained. With the abovementioned process it is possible to obtain a composition having granules with an average diameter less than 2 microns and a greater homogeneity than the known processes.

RELATED APPLICATIONS

This application is a 35 U.S.C. 371 national stage filing fromInternational Application No. PCT/IT2006/000613 filed Aug. 9, 2006, theteachings of which are incorporated herein by reference.

The present invention relates to a double-extrusion production processfor coating organic and inorganic pigments preferably with acrylic,aldehyde and/or ketone resins in order to provide a particle compositionpreferably in the form of granules.

As is known, pigments are solids both of an organic and an inorganicnature which are defined as such when they are used within a fixingsystem, such as resins, absorbing a part of the light and reflectingtheir complementary part which forms the colour of the coated surface.

As such, they are solids with a very irregular surface, which differsfrom pigment to pigment, and having the property of interfacing withother substances completely different from each other and greatlyinfluenced by the physical and chemical conditions of the contactelements.

Consequently, the formation of the colour, resulting from the mixture ofvarious pigments, is not uniform among the various preparations, due notonly to the change in environmental conditions, which vary in each case,but also the differences in properties of the surface of the pigment andthe surface tension properties of the polymers during melting which,even though not different from batch to batch, may vary slightly.

The difficulties of integrating pigments in vehicle systems based onwidely varying resins are well known.

This is true both in the case of powder systems, where contact of thepigment occurs with a polymer resin in the melted state inside anextruder, and in the case of liquid systems where interfacing occurswith polymers (resins) in the form of a solution, emulsion or dispersiondiluted both with solvents and/or water, which have a flocculatingeffect on the system.

At present in the formulations of powder paints, insertion of thepigments is performed by means of simple physical mixing of the saidpigments with granules of varying form (chips or flakes) of the resins,which form the vehicle with the addition of chemical additives able toimprove the contact between pigment and resin so as to integrate thepigment in the resin, during extrusion where melting of the resincontained in the mix and dispersion or milling of the pigment(s) in aliquid/viscous phase occurs.

This process normally uses single-screw extruders (single-screw Banderatype) which have a pigment milling capacity which is not sufficientlypowerful and therefore not exactly suitable for extruding organicpigments with a high calorimetric yield and for this reason are mainlyused for inorganic or organic pigments, but in products where formationof the colour and the calorimetric yield are not to be regarded asdecisive.

Twin-screw extruders with composite screws (Leistriz type) are normallyused and known; these, compared to single-screw extruders, provide abetter performance in terms of pigment refining and milling capacity andare therefore used whenever pigments which are difficult to mill areused and where a high calorimetric yield is required.

Both the single-screw and twin-screw extruders use heat supplied to theextrusion chamber in order to favour melting of the polymer and millingof the pigments in the liquid/viscous-phase.

Despite this, the use of twin-screw extruders has also proved to havelimitations in terms of dispersion capacity in the case whereparticularly sophisticated and costly organic pigments are used, such asthose developed for use in paints with a good resistance to externalagents, transparency for use in metallic paints, high colour tone andhigh saturation, and where it is required to maximize the degree ofdispersion and consequently the calorimetric yield; or also inorganicpigments which are particularly difficult to disperse or in both casessimply in order to be able to increase the concentration of the pigmentin the extruded preparations, while maintaining good results in terms ofdispersion.

In particular, with the methods known in the art, the fineness and thedegree of homogeneity of milling which can be achieved with many organicpigments (such as, for example, magenta dimethylquinacridone Red 122pigment, violet-red betaquinacridone Violet 19 pigment, orangediketo′pyrrolo-pyrrole Orange 73 pigment), are not acceptable forapplication sectors such as, for example, that of high-performancepaints.

The pigment particles remain, in fact, too large (i.e. 5-30 microns formagenta dimethylquinacridone Red 122 pigment, 10-30 microns forviolet-red betaquinacridone Violet 19 pigment, and 10-25 microns fororange diketo-pyrrolo-pyrrole Orange 73 pigment) as well as not beingdispersed in a sufficiently homogeneous manner, negatively affectingproperties such as the colorimetric yield, the brilliance and the tone.

In all these cases, a second extrusion in a hot extruder has notprovided a substantial improvement in the degree of dispersion.

The possible use of extruded solid preparations not only in powderpaints or as master batches in plastics, but also as solid substitutepreparations, by means of solubilization with solvent, of the millingstep, which is typical of liquid paints and inks, has accentuated thelimitations and needs mentioned above.

DESCRIPTION OF THE INVENTION

It has therefore been necessary to develop a novel extrusion process forcoating organic and/or inorganic pigments with resins, in order toobtain a formulation in the form of granules which allows the negativeaspects of the present situation to be overcome.

This technology, which forms the subject of the present invention, isbased on:

-   -   a first extrusion of the resin and pigment based mixture without        induced heating;    -   a second extrusion with induced heating of the mixture from the        first extrusion;    -   granulation of the mixture thus obtained.

According to one aspect of the invention, the first extrusion isperformed in a co-rotating twin-screw extruder which allows a first stepto be performed without induced heating, using only the heat developednaturally by the cutting and friction forces inside the extruder.

The twin-screw extruder preferred for the invention uses screws with adiameter of 27-110 mm, preferably 30-87 mm, and length 25-48 times thediameter, preferably 32-40 times.

The temperature inside the abovementioned extruder may vary from about 0to about 50° C., preferably from 5 to 35° C.; dividing ideally theinside of the extruder into 9 zones of identical length, the temperatureis normally set in the first three zones to 5/15° C., preferably 10° C.,in the second zones (3 to 6) to 15/25° C., preferably 20° C., and in thethird zones (6 to 9) to 25/35° C., preferably 30° C.

The temperature inside the extruder is controlled both by the coolingset in the first zones of the extruder and by evaporation of the waterpresent as a component of the mix; this is performed preferably by meansof a breather valve situated towards the end part in the extruderconveying zone. Control of the temperature is important for keeping themix in a not entirely melted state so that the cutting forces may exerttheir action more effectively.

The flowrate of the first extrusion is about 5-20 kg/h, preferably 10-15kg/h.

The semifinished product, in a shapeless but homogeneous solid state ofpigment and resin leaving the extruder after the first step, may containwater in large quantities, something which may make use thereof duringsubsequent extrusion difficult. In this case, it is preferable to add tothe mixture surfactants or dispersants (which are preferably non-ionic,such as epoxidized sorbitan and soy bean oil esters, preferablyepoxidized sorbitan ester), in order to favour wetting of the solidphase and provide a homogeneous mix with good extrudibilitycharacteristics.

The extrudate from the first extrusion is then transferred for secondaryextrusion; this procedure may be performed both in batches andcontinuously.

The second twin-screw extruder has screws with a diameter of 27-110 mm,preferably 30-87 mm, and length 30/60 times the diameter, preferably48-60 times the diameter.

The temperature inside the abovementioned extruder may vary from about50 to about 130° C., preferably from 80 to 110° C.; dividing ideally theinside of the extruder into 9 zones of identical length, the temperatureis normally set, by means of the supply of induced heat, in the firstthree extrusion zones to 70/90° C., preferably 80° C., in the secondzones (3 to 6) to 80/100° C., preferably 90° C., and in the third zones(6 to 9) to 90/110° C., preferably 100° C.

The flowrate of the first extrusion is 15-35 kg/h, preferably 20-30kg/h.

The extrusion process is completed using a die and pelletizer.

The remaining water present in the mix is extracted also by means ofapplication of a vacuum, if necessary, through the breather valve of thedegassing system.

The fineness of milling and homogenization of the dispersed particles iscompleted obtaining a very narrow distribution of the particle sizecurve with particle size values which are small and less than values of1-2 microns when measured using an optical microscope with ×200magnification.

The melted state of the mass output from the second operation will alsoallow the production of microgranules by means of a die andwater-cutting microgranulator mounted on the extruder head.

It should be emphasized that, while a single hot pass produces anirregular milling fineness with diffused presence of particles having asize of 5-30 microns, 10-30 microns, 10-25 microns in each case (whenmeasured using an optical microscope with ×200 magnification), a dualcold/hot pass not only reduces the size of the particles to less than1-2 microns, but also results in perfect uniformity thereof (narrowdistribution of the particle size curve) and consequently a highercalorimetric yield.

In particular, in the case of formulations based on both inorganic andorganic pigments, an aqueous solution of the dispersant is prepared (thewater is preferably used in quantities ranging between 10 and 20%relative to the total weight of the formulation); the resin isintroduced into the mixer (preferably an open receptacle of thehigh-speed blade type) and it is wetted with a quantity equal to about50% of said solution; the pigment is introduced while mixing and theremaining amount of aqueous solution is added; the inert filler is addedand, after mixing, the product is discharged and transferred to theextruder.

The mixture may also contain mineral reinforcing fillers, such as bariumsulphate for example.

Mixing, both in the case of organic pigments and in the case ofinorganic pigments, is normally performed at a speed of between 800 and2200 rpm.

The granular formulation which can be obtained according to the processof the present invention may be used for the production of granularsystems based on resin and pigment and known in the art, and inparticular those described in the international patent applicationsPCT/IT2005/000443, PCT/IT2005/000536, PCT/EP2006/000019 andPCT/IT2006/000588, in the name of the same Applicants and incorporatedherein by way of reference.

Description of the Plant/Process

The plant/process consists of:

a high-speed turbomixer with propeller impeller and number ofrevolutions ranging from 1000 to 3000 per minute, preferably 2000/2500rpm, which allows homogenization of the components consisting ofpigment(s), resin, additives and water.

A cooled co-rotating twin-screw extruder for the first pass (Leistriztype) suitable for obtaining a perfect cold dispersion of the pigmentsof the mixture from the turbomixer.

The “cold pass” does not supply heat and therefore avoids completemelting of the resin, but ensures, using only the “friction” heatproduced by the high cutting forces which are generated, a perfectdispersion of the pigment, nevertheless obtaining a non-granularshapeless physical form.

A heated co-rotating twin-screw extruder (Leistriz type) in which themixture melting process takes place, with complete outflow of theaqueous phase.

A microgranulator (Gala underwater pelletizing type) which is mounted onthe extruder head is used for microgranulation of the extrudate in theaqueous phase.

Preferably the granules are produced by means of a water jet cuttinggranulator of the type produced by Gala Industries Inc. and described ininternational patent application WO/21371, incorporated herein by way ofreference.

A sieving/drying system which consists essentially of a fluid-bedvibrating screen, for separation of the aqueous phase andsieving/screening of the granules from possible formations with aparticle size not to specification and associated drying by hot-airmeans.

The microgranules obtained from the extrusion process which depending onthe specific weight of the extruded mixture may have a number variablefrom 80 to 200 granules per gramme are supplemented with any silicafluidizing additive where required to avoid problems of compaction ofthe microgranules during storage or transportation in temperatureconditions which are not properly controlled and conveyed away forpackaging.

The examples which follow are intended to be purely illustrative andnon-limiting and identify some of the possible mixtures of compounds tobe supplied to the extruder in order to produce subsequently theparticle compositions of the invention both in granule and in powderform; the water must not obviously be regarded as a component of thefinal formulation since it is eliminated during the drying stage; theparts are to be regarded by weight.

Example 1

Conventional single-extrusion process Magenta dimethyquinacridone Red122 pigment: 25 Barium sulphate: 20 Atmer ® 116 (ethoxylated sorbitolester): 5 Laropal ® A 81 (aldehyde resin): 50 Water: 12 Extrusionparameters: Zones 1-3: temp. 80° C. Zone 4-6: temp. 90° C. Zones 7-9:temp. 100° C. Diameter of the screws: 30 mm Length of the screws: 1560mm Die and pelletizer mounted 15 kg/h Yield: Result: milling fineness:5-30 microns

Example 2

Double-extrusion process Magenta dimethylquinacridone Red 122 pigment:25 Barium sulphate: 20 Atmer ® 116 (ethoxylated sorbitol ester): 5Laropal ® A 81 (aldehyde resin): 55 Water: 12 Parameters of firstextrusion: Zones 1-3: temp. 10° C. Zones 4-6: temp. 20° C. Zones 7-9:temp. 30° C. Diameter of the screws: 30 mm Length of the screws: 750 mmDie and pelletizer not mounted 25 kg/h Yield: Parameters of secondextrusion: Zones 1-3: temp. 80° C. Zones 4-6: temp. 90° C. Zones 7-9:temp. 100° C. Diameter of the screws: 30 mm Length of the screws: 1560mm Die and pelletizer mounted 15 kg/h Yield: Result: milling fineness:1-2 microns

Example 3

Conventional single-extrusion process Violet-red betaquinacridone Violet19 pigment: 40 Barium sulphate: 10 Atmer ® 116 (ethoxylated sorbitolester): 6 Laropal ® A 81 (aldehyde resin): 44 Water: 12 Extrusionparameters: Zones 1-3: temp. 80° C. Zones 4-6: temp. 90° C. Zones 7-9:temp. 100° C. Diameter of the screws: 30 mm Length of the screws: 1560mm Die and pelletizer mounted 15 kg/h Yield: Result: milling fineness:10-30 microns

Example 4

Double-extrusion process Violet-red betaquinacridone Violet 19 pigment:40 Barium sulphate: 10 Atmer ® 116 (ethoxylated sorbitol sorbitol): 6Laropal ® A 81 (aldehyde resin): 44 Water: 12 Parameters of firstextrusion: Zones 1-3: temp. 10° C. Zones 4-6: temp. 20° C. Zones 7-9:temp. 30° C. Diameter of the screws: 30 mm Length of the screws: 750 mmDie and pelletizer not mounted 25 kg/h Yield: Parameters of secondextrusion: Zones 1-3: temp. 80° C. Zones 4-6: temp. 90° C. Zones 7-9:temp. 100° C. Diameter of the screws: 30 mm Length of the screws: 1560mm Die and pelletizer mounted 15 kg/h Yield: Result: milling fineness:1-2 microns

Example 5

Conventional single-extrusion process Orange diketo-pyrrolo-pyrroleOrange 73 40 pigment: Barium sulphate: 10 Atmer ® 116 (ethoxylatedsorbitol ester): 5 Laropal ® A 81 (aldehyde resin): 45 Water: 12Extrusion parameters: Zones 1-3: temp. 80° C. Zones 4-6: temp. 90° C.Zones 7-9: temp. 100° C. Diameter of the screws: 30 mm Length of thescrews: 1560 mm Die and pelletizer mounted 15 kg/h Yield: Result:milling fineness: 10-25 microns

Example 6

Double-extrusion process Orange diketo-pyrrolo-pyrrole Orange 73 40pigment: Barium sulphate: 10 Atmer ® 116 (ethoxylated sorbitol ester): 5Laropal ® A 81 (aldehyde resin): 45 Water: 12 Parameters of firstextrusion: Zones 1-3: temp. 10° C. Zones 4-6: temp. 20° C. Zones 7-9:temp. 30° C. Diameter of the screws: 30 mm Length of the screws: 750 mmDie and pelletizer not mounted 25 kg/h Yield: Parameters of secondextrusion: Zones 1-3: temp. 80° C. Zones 4-6: temp. 90° C. Zones 7-9:temp. 100° C. Diameter of the screws: 30 mm Length of the screws: 1560mm Die and pelletizer mounted 15 kg/h Yield: Result: milling fineness:1-2 microns

The invention claimed is:
 1. A process for the production of a particlecomposition containing at least one of aldehyde, ketone and acrylicresin, and at least one pigment, comprising the following steps: (a)extrusion, in a co-rotating twin-screw extruder, of a mixture containingsaid at least resin and said at least one pigment without inducedheating, using only the heat developed naturally by the cutting andfriction forces inside the extruder, wherein the temperature inside theextruder according to step (a) varies from 5 to 50° Celsius, and thescrews of the extruder according to step (a) have a length 20-40 25-48times the diameter, and wherein an extrudate leaves the co-rotatingtwin-screw extruder after step (a) and comprises a non-granulatedhomogenous mixture of the at least one resin and the at least onepigment; (b) subsequent extrusion, with induced heating, of the mixtureobtained from the extrusion according to step (a), wherein thetemperature inside the extruder according to step (b) varies from 80 to130° Celsius, and the screws of the extruder according to step (b) havea length 30-60 times the diameter; and (c) granulation of the mixturethus obtained, wherein the extrusion of step (a) comprises a pluralityof zones that are temperature controlled such that a temperature of atleast one zone is set to a temperature within a range of from 10 to 15°C. and wherein the temperature of one or more zones of the firstextrusion step is controlled with at least a cooling set, and whereinthe extrusion of step (b) comprises a plurality of zones that aretemperature controlled such that a temperature of at least one zoneincreases from a temperature in a previous zone.
 2. The processaccording to claim 1, wherein step (b) is performed in a co-rotatingtwin-screw extruder.
 3. The process according to claim 2, wherein thescrews of the extruder according to step (a) have a diameter of 27-110mm.
 4. The process according to claim 3, wherein the screws of theextruder according to step (a) have a diameter of 30-87 mm.
 5. Theprocess according to claim 3, wherein said screws of the extruderaccording to step (a) have a length 25-40 times the diameter.
 6. Theprocess according to claim 5, wherein said screws of the extruder tostep (a) have a length 32-40 times the diameter.
 7. The processaccording to claim 1, wherein the temperature inside one or more zonesof the extruder according to step (a) varies from 5 to 35° C.
 8. Theprocess according to claim 1, wherein the flowrate of the extrusionaccording to step (a) is 5-20 kg/h.
 9. The process according to claim 1,wherein the flowrate of the extrusion according to step (a) is 10-15kg/h.
 10. The process according to claim 2, wherein the screws of theextruder according to step (b) have a diameter of 27-110 mm.
 11. Theprocess according to claim 10, wherein the screws of the extruderaccording to step (b) have a diameter of 30-87 mm.
 12. The processaccording to claim 1, wherein said screws of the extruder to step (b)have a length 48-60 times the diameter.
 13. The process according toclaim 1, wherein the temperature inside the extruder according to step(b) varies from 80 to 110° C.
 14. The process according to claim 1,wherein the flowrate of the extrusion according to step (b) is 15-35kg/h.
 15. The process according to claim 14, wherein the flowrate of theextrusion according to step (b) is 20-30 kg/h.
 16. The process accordingto claim 1, wherein the granulation is performed by means of cuttingwith a water jet.
 17. The process according to claim 1, wherein thegranulation is performed by means of cutting with a water jet.
 18. Theprocess according to claim 1, wherein said at least one pigment isorganic and/or inorganic.
 19. The process according to claim 18, whereinsaid further comprising a mineral filler and wherein the mineral filleris a barium sulphate.
 20. The process according to claim 1, wherein themixture further contains at least one dispersant.
 21. The processaccording to claim 20, wherein said dispersant is non-ionic.
 22. Theprocess according to claim 20, wherein said dispersant is selected fromthe group consisting of epoxidized sorbitan and soy bean oil esters. 23.The process according to claim 22, wherein said dispersant is theepoxidized sorbitan ester.
 24. The process according to claim 1, whereinsaid mixture further contains water.